The present invention relates to a fingerprint authentication system, a fingerprint authentication method, and a fingerprint authentication program.
In recent years, fingerprint authentication has gained attention as an authentication method for recognizing individuals. Fingerprints differ from person to person and do not vary over time. Accordingly, fingerprint authentication is more reliable than currently widespread password authentication and so on. With fingerprint authentication, however, it is necessary to prevent fraudulent behavior whereby the fingerprint of another individual is taken and the individual is impersonated using a forged false finger or the like. Following Patent Documents 1 and 2, for example, disclose a technique for preventing this fraudulent behavior by detecting a false finger using a color of a surface of the finger when irradiated with light as a reference. Further, in Patent Document 3, a false finger is detected by irradiating a finger with light from above and capturing an image of light transmitted through the interior of the finger. Furthermore, in Patent Document 4, light is emitted from a side of a finger, and a diffusion pattern of light transmitted through the interior of the finger is used to detect a false finger formed by attaching a thin film having a forged fingerprint thereon to the surface of the finger.
Moreover, a technique of extracting lines known as ridges in order to compare fingerprints exists. In Patent Document 5, for example, a ridge can be extracted with stability even when a fingerprint includes wrinkles and noise by performing frequency analysis in respective local regions, selecting ridge candidates in the form of peaks within a frequency space, and determining a ridge (a peak) from a continuity of the ridge.    Patent Document 1: Patent Publication JP-A-2003-50993    Patent Document 2: Japanese Patent Publication No. 2637253    Patent Document 3: Patent Publication JP-A-9-134419    Patent Document 4: Patent Publication JP-A-2007-249296    Patent Document 5: Japanese Patent Publication No. 2739856
With the technique described in Patent Documents 1 and 2, in which a false finger is detected using the color of the surface of the finger as a reference, and the technique described in Patent Document 3, in which a false finger is detected by irradiating a finger with light from above, a false finger formed by attaching a transparent thin film having a copy or the like of a fingerprint of another individual thereon to the surface of a finger cannot be detected. The reason for this is that with Patent Documents 1 and 2 it is difficult to differentiate between the color of the surface of the false finger to which the transparent thin film is attached and the color of skin, while with Patent Document 3, an attenuation factor of the light transmitted through the transparent thing film is low, making it difficult to differentiate between the light transmitted through the interior of the finger and the thin film and the light transmitted only through the interior of the finger.
With the technique described in Patent Document 4, in which a false finger is detected by irradiating a finger with light from a side, the light may not be emitted directly onto the transparent thin film attached to the surface of the finger, and in this case, the false finger cannot be detected, similarly to Patent Document 3. For example, when the finger is pressed against a fingerprint sensor surface, a part of the finger may cover a periphery of the thin film such that the light to be emitted onto the thin film is blocked by this part of the finger. In this case, the light is not emitted directly onto the thin film, and therefore a similar condition to that of Patent Document 3 occurs. In this condition, it is difficult to differentiate between the light transmitted through the interior of the finger and the thin film and the light transmitted only through the interior of the finger.